Don't think so, guess it should be reasonable to do a `grep -r CONFIG_CHECK /var/db/pkg -l` and then have some algorithm that sources these ebuilds and parses those CONFIG_CHECK variables. Not sure if CONFIG_CHECK is the sole way to check config parameters.

I have a question, let's say I emerge package which need specific kernel configuration (some CONFIG_* needs to be selected) and later on during kernel upgrade I will unchecked this option. How to check whole system (all packages) if all kernel configuration is provided, is there any gentool for it?

emc ... there isn't such a tool, it would be extremely difficult to make such a thing. Take for example a package like wpa_supplicant, it can run as a ieee802.1x supplicant, and so only require an ethernet driver, in other usage it might require CFG80211/MAC80211, a wireless driver, RFKILL, and other CONFIG options perhaps specific to that card (LEDS, or USB_SERIAL, for instance). Then there is the question of which driver, and all the dependencies of that driver (eg, for a USB ethernet/wireless card, PCI, etc, etc). How would such a tool figure out which specific usage you had in mind when installing wpa_supplicant (and note, this is just one package of many).

Other packages such as say net-libs/libpcap have a netlink useflag and so would require CONFIG_NETFILTER_NETLINK, but it would require a lot of checks against packages, useflags, etc, to then come to the conclusion that this was in fact needed, and some useflags such as 'hardened' can be used without having grsec or selinux enabled in the kernel, so it makes the whole process of parsing out data from useflags and correlating them with config option next to impossible.

So, such a tool (should someone try to code such a thing) would more likely come up with false positives, suggest the wrong options, etc, etc ... and as the kernel is a moving target the tool would need to be constantly updated and know and understand each kernel revision, in all quite an impossible task, specifically if such a tool was for use with portage (another moving target).